H2O-Enabled Reversible SO2 Resistance on Separately Dual-Functional Pd-W Sites for Low-Temperature Hydrocarbon Oxidation.

Sulfur dioxide (SO2) poisoning remains a critical challenge for noble-metal catalysts in hydrocarbon oxidation, particularly under industrial humid conditions. H2O is commonly regarded as a detrimental component in SO2-containing exhaust streams where sulfur-water synergistic deactivation prevails. Here we prove that, when combined with rational active-site design, H2O molecules can instead promote SO2-resistance in hydrocarbon oxidation catalysis. A Pd/W-Al2O3 catalyst with spatially separated Pd and W sites exhibits superior low-temperature methyl ethyl ketone (MEK) oxidation activity and unprecedented resistance to SO2 poisoning under both dry and humid conditions. In the absence of water, SO2 is selectively immobilized as SO32- species on W sites, preventing competitive adsorption on Pd and preserving MEK oxidation pathways. Under humid conditions, however, SO2 can be transformed into HSO3- species that interact directly with Pd-bound ketone intermediates. Spectroscopic and theoretical investigations reveal that HSO3- functions as a dynamic proton shuttle, enabling a proton-bridge-assisted C-C bond cleavage pathway that facilitates intermediate conversion and drives reversible recovery from SO2 poisoning. This work demonstrates how H2O molecules fundamentally reshape SO2-catalyst interactions and highlights a general strategy for converting SO2 poisons into reaction promoters through spatially separated dual-functional active sites.